First, this is a "calc and beyond" and this is a trig question. Second, call the argument something like u. The problem "looks" a whole lot easier this way. Next try chaning the tangent function into another form, namely sines and cosines. You'll find the answer falls out rather quickly.

Ouch! You probably learnt that multiplying by 8 on one side, is dividing by it on the other side.
However: there's the -3 that has to go first! It's better to remember the rules:
- you may multiply both sides with a non-zero number
- you may add the same number to both sides

Now, if you'd want to get rid of the 8, you'd have to multiply both sides with 1/8, but that would also give -3/8 on the right side, and no longer a -3.
What you would probably do is first add 3 to both sides (i.e. changing sides of -3), giving 1+3 = 8cos(2x + 1). Now you can remove the 8, giving:

4/8 = cos(2x + 1) <=> cos(2x + 1) = 1/2.

And a cosine can surely be 1/2, so this will have a solution, actually two.
You're making the same mistake with the tan-equation.